1. Field of the Invention
This invention relates to electrical resistor assemblies incorporating a plurality of forced ventilated resistor grids that are used in the dynamic braking or retarding function of large electric motors such as the direct current traction motors on diesel electric locomotives. The resistor grid of the present invention has a zigzag resistor that is formed from a plurality of resistor elements that are connected to each other by welded joints of various types.
During dynamic braking of a diesel electric locomotive, its traction motors operate in a generating mode and supply current to heavy duty resistor grids where the electrical energy is converted to heat and dissipated to the atmosphere with the aid of cooling fans. The zigzag resistor elements must be able to withstand the high temperatures and vibration inherent in being utilized on locomotives. Further, in order to be economically useful, the resistor grids must be efficiently assembled and be easily replaceable in use.
2. Description of the Prior Art
Conventionally, the resistor element within the resistor grid is made up of a folded or zigzag strip or strips of resistance material mounted in the grid frame. The resistor strip may be a unitary fan folded strip as is shown in U.S. Pat. No. 4,100,526 and U.S. Pat. No. 4,651,124. The resistor element may also be formed from a series of short sections that are welded together as shown in U S. Pat. No. 4,651,125; U.S. Pat. No. 4,654,627; U.S. Pat. No. 5,068,637; and U.S. Pat. No. 5,049,852.
The present invention is directed to an improved resistor grid that has the zigzag strip made up of a plurality of resistor elements which are joined to each other by welded joints.